cmd/go: remove GOAMD64 environment variable

This removes the GOAMD64 environment variable and its documentation.
The value is instead supplied by a compiled-in constant.

Note that function alignment is also dependent on the value of
the (removed) flag; it is 32 for aligned jumps, 16 if not.
When the flag-dependent logic is removed, it will be 32.

Updates #35881.

Change-Id: Ic41c0b9833d2e8a31fa3ce8067d92aa2f165bf72
Reviewed-on: https://go-review.googlesource.com/c/go/+/231600
Reviewed-by: Austin Clements <austin@google.com>

src/cmd/dist/build.go

@@ -31,7 +31,6 @@ var (
 	goos             string
 	goarm            string
 	go386            string
-	goamd64          string
 	gomips           string
 	gomips64         string
 	goppc64          string
@@ -152,12 +151,6 @@ func xinit() {
 	}
 	go386 = b
 
-	b = os.Getenv("GOAMD64")
-	if b == "" {
-		b = "alignedjumps"
-	}
-	goamd64 = b
-
 	b = os.Getenv("GOMIPS")
 	if b == "" {
 		b = "hardfloat"
@@ -230,7 +223,6 @@ func xinit() {
 
 	// For tools being invoked but also for os.ExpandEnv.
 	os.Setenv("GO386", go386)
-	os.Setenv("GOAMD64", goamd64)
 	os.Setenv("GOARCH", goarch)
 	os.Setenv("GOARM", goarm)
 	os.Setenv("GOHOSTARCH", gohostarch)
@@ -1171,9 +1163,6 @@ func cmdenv() {
 	if goarch == "386" {
 		xprintf(format, "GO386", go386)
 	}
-	if goarch == "amd64" {
-		xprintf(format, "GOAMD64", goamd64)
-	}
 	if goarch == "mips" || goarch == "mipsle" {
 		xprintf(format, "GOMIPS", gomips)
 	}

src/cmd/dist/buildruntime.go

@@ -42,7 +42,6 @@ func mkzversion(dir, file string) {
 //
 //	const defaultGOROOT = <goroot>
 //	const defaultGO386 = <go386>
-//	const defaultGOAMD64 = <goamd64>
 //	const defaultGOARM = <goarm>
 //	const defaultGOMIPS = <gomips>
 //	const defaultGOMIPS64 = <gomips64>
@@ -72,7 +71,6 @@ func mkzbootstrap(file string) {
 	fmt.Fprintf(&buf, "import \"runtime\"\n")
 	fmt.Fprintln(&buf)
 	fmt.Fprintf(&buf, "const defaultGO386 = `%s`\n", go386)
-	fmt.Fprintf(&buf, "const defaultGOAMD64 = `%s`\n", goamd64)
 	fmt.Fprintf(&buf, "const defaultGOARM = `%s`\n", goarm)
 	fmt.Fprintf(&buf, "const defaultGOMIPS = `%s`\n", gomips)
 	fmt.Fprintf(&buf, "const defaultGOMIPS64 = `%s`\n", gomips64)

src/cmd/go/alldocs.go

@@ -1754,9 +1754,6 @@
 // 	GO386
 // 		For GOARCH=386, the floating point instruction set.
 // 		Valid values are 387, sse2.
-// 	GOAMD64
-// 		For GOARCH=amd64, jumps can be optionally be aligned such that they do not end on
-// 		or cross 32 byte boundaries.  Valid values are alignedjumps (default), normaljumps.
 // 	GOMIPS
 // 		For GOARCH=mips{,le}, whether to use floating point instructions.
 // 		Valid values are hardfloat (default), softfloat.

src/cmd/go/internal/cfg/cfg.go

@@ -241,7 +241,6 @@ var (
 	// Used in envcmd.MkEnv and build ID computations.
 	GOARM    = envOr("GOARM", fmt.Sprint(objabi.GOARM))
 	GO386    = envOr("GO386", objabi.GO386)
-	GOAMD64  = envOr("GOAMD64", objabi.GOAMD64)
 	GOMIPS   = envOr("GOMIPS", objabi.GOMIPS)
 	GOMIPS64 = envOr("GOMIPS64", objabi.GOMIPS64)
 	GOPPC64  = envOr("GOPPC64", fmt.Sprintf("%s%d", "power", objabi.GOPPC64))
@@ -267,8 +266,6 @@ func GetArchEnv() (key, val string) {
 		return "GOARM", GOARM
 	case "386":
 		return "GO386", GO386
-	case "amd64":
-		return "GOAMD64", GOAMD64
 	case "mips", "mipsle":
 		return "GOMIPS", GOMIPS
 	case "mips64", "mips64le":

src/cmd/go/internal/help/helpdoc.go

@@ -582,9 +582,6 @@ Architecture-specific environment variables:
 	GO386
 		For GOARCH=386, the floating point instruction set.
 		Valid values are 387, sse2.
-	GOAMD64
-		For GOARCH=amd64, jumps can be optionally be aligned such that they do not end on
-		or cross 32 byte boundaries.  Valid values are alignedjumps (default), normaljumps.
 	GOMIPS
 		For GOARCH=mips{,le}, whether to use floating point instructions.
 		Valid values are hardfloat (default), softfloat.

src/cmd/internal/objabi/util.go

@@ -37,16 +37,13 @@ var (
 
 const (
 	ElfRelocOffset   = 256
-	MachoRelocOffset = 2048 // reserve enough space for ELF relocations
+	MachoRelocOffset = 2048           // reserve enough space for ELF relocations
+	Go115AMD64       = "alignedjumps" // Should be "alignedjumps" or "normaljumps"; this replaces environment variable introduced in CL 219357.
 )
 
+// TODO(1.16): assuming no issues in 1.15 release, remove this and related constant.
 func goamd64() string {
-	switch v := envOr("GOAMD64", defaultGOAMD64); v {
+	return Go115AMD64
-	case "normaljumps", "alignedjumps":
-		return v
-	}
-	log.Fatalf("Invalid GOAMD64 value. Must be normaljumps or alignedjumps.")
-	panic("unreachable")
 }
 
 func goarm() int {

src/internal/cfg/cfg.go

@@ -33,7 +33,6 @@ const KnownEnv = `
 	GCCGO
 	GO111MODULE
 	GO386
-	GOAMD64
 	GOARCH
 	GOARM
 	GOBIN